Apparatus for making plastic masses



Nov. 9, 1948. w. ShBOHLMAN ETAL 2,453a404 APPARATUS FOR MAKING PLASTIC MASSES Filed June 1, 1945 WALTER J. BOI-ILMAM/ DAV/D J. BRUCE INVENTORS ATT EY Patented Nov. 9, 1948 UNITED; STATES PATENT, OFFICE Walters. Bohlman, Wilmington, Del., and David 13S. Bruce, Lawr ence,' Kans.;rassignors, by mesne assignments; to United Statesof America as represented by the Secretary of War hpplicationjune 1, ls ia seri l N0.-597,030 iolaim. (01. 18 -2) This invention relates to an improved apparatus for making plastic masses, more particularly in the manufacture of colloided smokeless powder. 1 1

Double base smokeless powder is usually prepared by colloiding nitroootton and nitroglycerin with the aid of a mutual volatilefsolvent; such as acetone, alcohol and ether-or mixtures thereof. The solvent is subsequentlyremoved by evaporation.

The hazards of colloiding nitrocotton-nltroglycerin mixtures without the aid of solvents,- except in the special case where the nitrocotton is lim ited in amount to that'which will readily dissolve in the nitroglycerin as in making blasting gelatin and gelatin dynamites, have resulted largely in avoidance of solventlessjtypes of processesfor making such colloidized powders;

Cellulose derivatives, such as organic esters and others, have been plasticized by working between roll surfaces with plasticizingv agents xetc. LFillers and the like are incorporated with natural and synthetic rubber by working between .roll sur-- faces. In these casesmaterial that drops from the rolls maybe readily recovered andreturned to the rolls, in fact, the material is' usually stripped from the rolls by hand and returned to the rolls a number of times before complete plasticizing and/or in corporation is obtained.

The verynature of the constituents of double at the same time the difiiculties ofdoing so are increased.

Furthermore, double base powder formulations generally include solid substances such asinor:

constant over an extended period of time.

base powders establishes two sets of conditions i not present in the referred tocases. In the first place, the mass to be worked is very, tough and stiii and difiioult to work mechanically, adherence to the roll being variable and uncertain with resultant dropping of the charge from the rolls. In the second place, the operations of rolling such explosive compositions in the absence of solvents are extremely hazardous, especially on account of ignition of the material, re-

quiring a minimum of direct personal contact m (proximity) from the time. of placing the mate: rial on the rolls until the mass is colloided and removed from the rolls.

In working materials on roll assemblies, to

plasticize them, it is preferable to utilize two rolls ganic salts for purposes of reducing flash, aiding in ignition, and thelike. These substances, when incorporated in the form ofiinely ground solid particles usually possess corrosiveand/or erosive actions, upon metals. t

In attempting to adapt the usual rolls, particularly in difierential speed roll assemblies, to the manufacture-of double base smokeless powders, considerable difficulty has resulted from the lack of adherence between the composition and the roll surface, especially over extended periods of operation. In working smokeless powder com: positions to colloid same it is required that the roll surfaceexhibit good adhesive properties with respect to the powder, and that this adhesiveness as well as the exact shape ofthe surface remain The subsequent molding characteristics and then the ballistics properties of the molded (extruded) powder grain are influenced by the uniformity of ,the'colloiding step on the differential. speed roll assembly. This, in turn, is determined by thedegree to which the opposing roll surfaces maintain their spacial relationships andthe like. In order to maintain a uniform working condition on the roll assembly, it is imperative that the roll surface be highly resistant to corrosion anderosion when in use.

Now, in accordance with thisinvention, it has been discovered that a roll having a porous chromium surface possesses improved adherencefor plastic compositions and retains this characteristicandits physical dimensions to a high degree even when subjected to corrosive, and :erosive actions by constituents of formulations worked thereon. Further, it has been discovered that colloidable explosive compositions can be readily and advantageously colloided by working on a roll assembly, one roll of, which has a porous merals designate similar parts, and wherein;

Fig. 1 is a front elevation of the two-roll assembly showing the powder composition adhered to the front roll, the composition being 'cut away nitroglycerin mow'cier. in. accordance with this in part to show the roll surfacej Fig. 2is a cross' section of the roll assembly in u'setaken along" the line 2-2 of Fig. 1; Fig. 3 is a microscopic elevational view of a section of the roll surface shown in Fig. 1; and Fig. 4 is a a section'taken;

along line 4-4 of Fig. 3. The two-roll assembly shown in Fig. 1 and Fig. 2 has a front roll l0 having an electrodeposited plating of porous chromium H. The powdercomposition 12 being worked on the roll assembly is adhered to the front roll having the porous chromium surface. The b'ack'roll I4 is a metal roll having an abrasive-blasted rough surface on which is electrodeposited aplating of chromium. Suitable axial supporting means 15 are provided for therolls and suitable 'journalled means l 6 are provided for supplying a heating medium," such as steam, to

taining. the desired temperature. I.

, As'shovvn in the microscopic view in Fig 30f the porous chromium-plated surface of the front roll, the surface '8 t-is composed of an irregular pattern of indentations, including pits I"! and The exposed A roll for use in the differential rolling of a 3 plasticizable mass, for example, an explosive composition comprising about 51% nitrocellulose, 43% nitroglycerin and 1% potassium sulfate with small percentages of as tabilizer such as diphenylamine or ethyl centralite, and a wax,

such as can'delilla, had a roll surface length of about 30 inches and a diameter of about-"14 inches. A porous type of electroplated chromium surface was produced on'this roll by electrodeposition of the chromium froma plating bath of normal constitution, a suitable bath for the deposition consisting of 250 grams of chromic acid (CrOc) and 2.5-3.0 grams of sulfuric acid, perliter of aqueous solution. The chromium pectedly good results as compared with those obtained by the use of the usual rolls for working plastic masses.

The adherence of the composition to the porous chromium roll surface was increased greatly and remained auniform over the "entire surface. Further, rio slick areas developed,- characterized by low adhesion with the material, as was true of other surfaces previously roughened by the use ofabrasives, vetc.

' The; procedure for "colloiding a nitrocellulosetion; Fifty-onep'arts of nitrocellulose (13.25%

' N) oflintbasej about 43 parts of nitroglycerin,

about-3.-parts of diethyl phthalate, about 1 part of ethyl oentralite, all parts by weight, and a small amount of carbonblack and candelilla wax, were made into a wet paste by known methods. The wetpaste was airdried to about. 12-44% moisture content and-then blended and uniformly mixed withabout: one partby weight of crushed solid potassium sulfate to give the final dry paste.

The dry paste was dumped from a fiber bucket, in a .G-gpoundncharge; ontoi-a' setpof. differential speed.rolls,-which rolls were 14 inches in diameter, and 30 incheslong, and maintained at 210 F. by circulating hot water. The rolls :were

the interior of the rolls for the purpose ofmainhorizontally disposed and the front or faster roll;..which--was ai'roll in accordance with. this invention and. hadla .;porous-type chromiump-lated surface, rotated at 31'R/P. M. (114 feet 'perminute) :and the diiierential ratio was 1.2:1. Thebaok roll had-a chrome plate electrodeposited on' a grit-blasted! metalroll. Thelcomposition was thus'subjected to periodic'or cylically chang ing pressure andxshearing actions as it adhered to and moved with the porous chromiumeplated roll surface, being alternately passed through confined Zone and an'unconfined zone. The rolling time was 2. minutes and the sheet thickness was 0;065-0;0.701inch. The/sheet of explosive compositionixwas' formed on the front or faster roll with excellent adherence and, .at thev end of the rolling time; thesheet' was cut offby means of a remotely. controlled air-operated doctorblade; The sheet a was carried by an automatic conveyor past cooling air blasts to a transfer trough. The

excellent adherenceof the composition to the front roll made it 'unnece'ssary for the operator to return to the machine to re-feed anyfragments ofthe init aicharge;

' Theforegoing explosive composition formed a very tough, stiff,co1loided mass. Experience has waselectrodeposited on the roll by a usual meth od for eifecting uniform electroplating of chromium and which will be well known to one familiar with the art.

After the electroplate wasdeposited .the

roll surface, the plating was etched anodically in a similar solution, following the'method of U. S. Patent No. 2,314,604. By this'method, the porosity of the plate was developed to yield a chromium surface having a multiplicity .of mi- I used ina roll assembly for working theexplosive composition described hereinabove, gave unexshown such. formulations tobe' exceedingly difficult to work onthe usual differential speed rolls, considerable'diificulty being experienced in preventing'the material from falling from the rolls. The improvement in accordance with the present invention can" be attributed; in part, tothe greateradhesiveness between the explosive com position and the porous chromium-surface.

The porous chromium-plated roll may be used with advantage in. working and 'colloiding' other formulations as well. The porous chromium surface isparticularly advantageouswith'other mixtures when they contain finely-"ground solid particles,--such as potassiumfsulfate, potassium ni- 7 trate,- e'tc.- The increased hardness of 'the plate reduces the'wearirig actioh of the solid thereon which" possibly accounts partially for so-called slick a'reas.

It may-be observedthat where fslick areas develop; the "composition may even shift to and move with the back roll.

The porous chromium electroplate may be prepared by developing a normal hard chromium plate on the underlying metal and then etching by chemical and/or electrochemical methods, the conditions selected for developing the porosity of the chromium plate being determined by the particular type of porosity desired. The most advantageous porosity will depend upon the physical nature of the composition to be worked.

In working the mass described above, it is preferred to use a porous chromium surface having plateaus with relatively small areas (pitted-type) surface produced by electrodeposition on a normalsurface followed by chemical and electrochemical etching separately or in combination and referred to herein as porous chromium electroplate.

The combination of a grit-blasted chromiumplated back roll with a pitted-type porous chromium-plated front or faster roll has been. found to be especially advantageous in working stifi and tough compositions in that there are good positive feeding action (bite), excellent adhesion over a long period of time, and improved colloiding action on the composition while being Worked.

Thus, an improved method has been discovered for colloiding or plasticizing colloidable mixtures, such as smokeless powder compositions, on roll assemblies, which comprises working the mixture on a differential speed roll assembly, the faster roll having a porous chromium electroplated surface with a high degree of afiinity or improved adhesiveness for the material being colloided whereby it is held onto and carried by the faster roll and is more efiiciently colloided and with considerably less hazard. The porous chromiumplated roll gives an improved plasticizing effect on plastic or plasticizable masses and is especially useful in differential speed rolling because of its greater adhesiveness for stiff colloidable materials, its resistance to corrosion, and its resistance to abrasion.

What we claim and desire to protect by Letters Patent is:

A diiferential speed rollassembly which comprises a pair of rolls adapted to rotate in opposite directions, one of said rolls adapted to rotate with a greater surface linear velocity than the. other of said rolls, said one of said rolls being provided with an outside surface of porous chromium electroplate characterized by high resistance to corrosion and erosion and having an improved adherence for a nitrocellulose-nitroglycerinpowder composition, and said other of said rolls being provided with a chromiumelectroplate deposited on an abrasive-blasted metallic surface.

WALTER S. BOHLMAN. DAVID S. BRUCE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Great Britain 1865 Germany Feb. 15, 1913 OTHER REFERENCES Modern Electroplating, The Electrochemical Soc. Special V01. (1942), pages 134, 135, 141 and 14 2. (Copy in Div. 56.)

Modern Electroplating, The Electrochemical Soc. Special Vo1., pages 134, 135, 1942. (Copy in Div. 56.)

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